In recent years, with increasing demand for lowering fuel consumption of automotive vehicles, automotive vehicles provided with idle stop functions and hybrid vehicles have become commercially practical. Such a vehicle requires a pump drive source in addition to an internal combustion engine, because various pumps driven by the internal combustion engine are at rest when the internal combustion engine is at rest. Especially, in cases of automotive vehicles provided with idle stop functions and hybrid vehicles, an oil pump is required to ensure oil pressure of a hydraulic mechanism controlling a transmission. In view of the foregoing, an electric oil pump, which applies a torque to a pump rotor by an electric motor, tends to be in increasing use.
Conventionally, as an electric oil pump mounted in a transmission of an automotive vehicle, a trochoid type internal gear pump is frequently adopted. The internal gear pump is a pump in which a pump rotor is rotated by a drive rotation shaft driven by an electric motor, and an outer rotor having internal teeth meshing with external teeth of the pump rotor is thereby rotated, so that a plurality of chambers formed between the internal teeth of the outer rotor and the external teeth of the pump rotor continuously vary in volume, and thereby suck and discharge working oil. Such an electric oil pump is described in JP 2012-207638 A (patent document 1), for example.
An electric oil pump includes: a drive control section for controlling energization to an electric motor; a stator part including a winding and an iron core for generating a magnetomotive force by energization from the drive control section; a rotor part in a space inside the stator part, including a permanent magnet, and configured to be rotated by the magnetomotive force; a drive rotation shaft fixed by press fitting or the like to the rotor part, and configured to rotate integrally with the rotor part; and a pump rotor part fixed by press fitting or the like to the drive rotation shaft, and configured to rotate integrally with the drive rotation shaft. A bearing part for the drive rotation shaft is formed with an oil groove for introducing working oil from a discharge part, and thereby forming an oil film on a rotation slide surface of the drive rotation shaft.